Cardiovascular disease (CVD) remains the major cause of mortality and morbidity in both type 1 (T1D) and type 2 (T2D) diabetes patients; modifications of traditional CVD risk factors have had a limited impact. This project called Regadenoson Blood flow in Type 1 Diabetes (RABIT1D) and is proposed as a sub-study of the Coronary Artery Calcification in Type 1 Diabetes (CACTI) study, which has established a unique cohort of 656 T1D patients (age 20-55, minimal diabetes duration of 10 yrs) and 764 non-diabetic controls. This cohort is being followed for progression of coronary artery calcification (CAC) measured using the electron beam tomography (EBT) for development of clinical CVD. Participants have been well characterized during the baseline examination (4/00-3/02) and two follow-up re-examinations 3 and 6 years later. The study has provided important insights into the risk factors and possible prevention of premature CVD in T1D. We are proposing assess a subset of this population to determine vasodilatory reserve as it relates to early coronary atherosclerosis in T1D.